Is space finite ?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Mark Turner, Jul 3, 2019.

  1. Mark Turner Registered Senior Member

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    Hello ,

    Is space finite ?

    What is the edge of space if there were one ?

    Thanks in advance for your opinions
     
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  3. DaveC426913 Valued Senior Member

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    We are not currently certain whether the universe is finite of infinite.

    We do define the Observable Universe as finite - it is simply the volume that we can see based on the propagation of light, Cosmological Expansion and the time since the Big Bang.

    Regardless of finite or infinite, the universe does not have an edge or a boundary. It is not an expansion into something, it is an expansion of space.
     
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  5. Mark Turner Registered Senior Member

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    How do we measure it ?

    Thanks in advance .
     
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  7. DaveC426913 Valued Senior Member

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    Measure what, exactly?
    The extent of the observable universe? It is limited by the speed of light and Cosmological expansion. We believe it is about 93 billion light years across. This gets a bit tricky, since the universe is only 13.7 billion years old.

    We have no way to know if there is more universe beyond that.
     
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  8. paddoboy Valued Senior Member

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    The expansion is measured by the cosmological red shift.
    The expansion acts to stretch light waves as they propagate, and we observe a shift towards the red end of the spectrum. A galaxy's/Quazar's actual distance from us, is related to how fast the universe is expanding.
    Cosmologists also use what we call "standard candles" such as type 1a supernova and Ceipheid variables which have apparent intrinsic brightness.
     
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  9. Mark Turner Registered Senior Member

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    You've answered my question thank you , on how we measure the size of the Universe and how big it is .

    I have one more question on cosmology.

    What matter exists between planets ?

    Thanks in advance .
     
  10. DaveC426913 Valued Senior Member

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    Space is pretty close to hard vacuum. Depending on where you look, it might have a few to many atoms floating around in every square inch.

    It's thicker in our solar system, where there's lot of dust and gas from planets, from the Sun and freely floating in their own orbits.

    Near Earth, 5 atoms per cubic centimetre is a good approximation.
    In intergalactic space, one atom per cubic metre is a good approximation.

    But the short answer to your question is: there is nearly - but not entirely - zero matter in most of space.
     
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  11. Mark Turner Registered Senior Member

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    Sorry , I need to bother you furthermore and extend the question .

    Is there a specific difference between matter and the Earths magnetosphere ?

    Thanks in advance.
     
  12. DaveC426913 Valued Senior Member

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    You do not need to apologize for asking questions. Questions are why some of us are here!

    Can you clarify your question? The Earth's magnetosphere is an electromagnetic field, just like that generated by any iron magnet; it is not matter (though, in both cases, it is generated by matter).
     
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  13. Mark Turner Registered Senior Member

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    329
    Alright , thank you , you did understand the question.

    How far does the electromagnetic field extend into space ?

    Is the field a form of energy ?

    Thanks in advance .
     
  14. DaveC426913 Valued Senior Member

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    Theoretically infinite. But its strength drops off as the cube of the distance. So, at double the distance it's 1/8th as strong. At 4x the distance its 1/64th as strong.

    No. It is one of the four fundamental forces of nature, along with the strong nuclear force, the weak nuclear force, and gravity.

    It is possible to interact with it to do work, but that's not the same as a source of energy.

    You can make things move with a magnet by moving the magnet around, but you cannot use a magnet alone as an energy source. You're really just converting mechanical energy into other forms of energy.
     
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  15. Mark Turner Registered Senior Member

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    Thank you for the explanation .

    In recapping what you've said ;

    The size of the potential Universe is unknown and unspecified , the observable space contains bodies / matter and between the bodies there is very little matter but the space contains electromagnetic fields .

    Have I understood you correctly ?

    Thanks in advance .
     
  16. DaveC426913 Valued Senior Member

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    Yep.
     
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  17. Mark Turner Registered Senior Member

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    Thank you DaveC , you've been very helpful with your explanations .

    I've no further questions on cosmology at this time .
     
  18. river

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    Space is infinite .

    Space can never not be .
     
  19. paddoboy Valued Senior Member

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    Just to add to Dave's excellent answers, we also refer to the topology of the universe/spacetime....that is whether it is flat, open [curved like a saddle] or closed [curved like a globe.] According WMAP the universe is flat to within small error bars. Flat meaning that if two beams of light are emitted parallel, they remain parallel. Or that any large triangle will have its angles add up to 180 degrees. That would not be the case if it were open or closed. Still, the possibility of some curvature over scales large enough to be outside the range of the error bars is real. And of course the universe as a whole, is far far bigger the the observable universe, so the flatness solution, based on today's technology, still leaves open the question of whether the universe is finite or infinite.
    https://phys.org/news/2017-06-universe-flat-topology.html

    Questions may arise as to what is the universe expanding into? The answer of course is that the universe is not expanding into anything..By definition, the universe is all there is and it is simply expanding. There's no outside the universe and no edges or centers to speak of, other then our observable center.
    While they may sound counter-intuitive, they are exactly what our models tell us at this time...
    And as Dave said, as long as you are genuine, and prepared to learn without any agenda, there are no stupid questions.
     

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